[Qgis-user] Q calculates Area incorrectly

[Chavoux Luyt]

Hi John,

On Fri, 8 Jan 2021, 22:01 , <qgis-user-request at lists.osgeo.org> wrote:

>
> From: <johnparrottca at gmail.com>
> To: <Qgis-user at lists.osgeo.org>
> Cc:
> Bcc:
> Date: Fri, 8 Jan 2021 08:24:33 -0000
> Subject: [Qgis-user] Q calculates Area incorrectly
>
> A colleague digitised a number of polygons on my laptop 3 years ago.
>
> I just loaded these on my desktop and used Q (3.16.2) to calculate areas,
> but they report incorrectly.
>
I found in my data that using an area-conserving projection (e.g. Albers
Equal Area) vs. a shape, direction or distance preserving projection (e.g.
UTM) made a significant difference in calculated areas (e.g. home range
sizes). It is often important to use the correct projection for the
question you want to answer, something that caught me a little bit by
surprise. Also look at the units of the projection you use... I am not sure
how much recent versions of QGIS have changed in this regard, but it could
be giving you the area in "square degrees" or "square meters" when you are
expecting "square km" or "hectares".

HTH

Cheers,
Chavoux Luyt
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